Many forms of turbomachinery comprise a gas acting on, or being acted upon, a plurality of airfoils. Examples of such turbomachinery include, but are not limited to, fans, propellers, windmills, compressors and turbines. For convenience of description, application of the presently disclosed embodiments to an aircraft mounted auxiliary power unit (APU) gas turbine engine is used herein by way of example, but the presently disclosed embodiments will find application in many forms of turbomachinery.
FIG. 1 schematically illustrates a portion of an APU, indicated generally at 10. APU 10 includes a turbine assembly 12 including impeller blades 14 contained therein. The impeller blades 14 pull air into the turbine assembly 12 from an air inlet duct 16. An air inlet screen 18 is provided between the air inlet duct 16 and the impeller blades 14 in an effort to prevent damage to the impeller blades 14 from soft foreign object ingestion (such as, for example, liquid or ice). Even with the provision of the air inlet screen 18, foreign object ingestion still causes damage in many APU installations in the field. This damage typically originates through operator procedures such as gate de-icing of the aircraft or maintenance water washing of the aircraft.